Regulation of cell proliferation, differentiation, and migration is important for the formation and function of tissues. Regulatory proteins such as growth factors control these cellular processes and act as mediators in cell-cell signaling pathways. Growth factors are secreted proteins that bind to specific cell surface receptors on target cells. The bound receptors trigger intracellular signal transduction pathways which activate various downstream effectors that regulate polynucleotide expression, cell division, cell differentiation, cell motility, and other cellular processes. Some of the receptors involved in signal transduction by growth factors belong to the large superfamily of G-protein coupled receptors (GPCRs) which represent one of the largest receptor superfamilies known.
GPCRs are biologically important as their malfunction has been implicated in contributing to the onset of many diseases, which include, but are not limited to, Alzheimer's, Parkinson, diabetes, dwarfism, color blindness, retinal pigmentosa and asthma. Also, GPCRs have also been implicated in depression, schizophrenia, sleeplessness, hypertension, anxiety, stress, renal failure and in several cardiovascular, metabolic, neuro, oncology and immune disorders (F Horn, G Vriend, J. Mol. Med. 76: 464–468, 1998.). They have also been shown to play a role in HIV infection (Y Feng, C C Broder, P E Kennedy, E A Berger, Science 272:872–877, 1996).
GPCRs are integral membrane proteins characterized by the presence of seven hydrophobic transmembrane domains which together form a bundle of antiparallel alpha (a) helices. The 7 transmembrane regions are designated as TM1, TM2, TM3, TM4, TM5, TM6, and TM7. These proteins range in size from under 400 to over 1000 amino acids (Strosberg, A. D. (1991) Eur. J. Biochem. 196: 110; Coughlin, S. R. (1994) Curr. Opin. Cell Biol. 6: 191–197). The amino-terminus of a GPCR is extracellular, is of variable length, and is often glycosylated. The carboxy-terminus is cytoplasmic and generally phosphorylated. Extracellular loops of GPCRs alternate with intracellular loops and link the transmembrane domains. Cysteine disulfide bridges linking the second and third extracellular loops may interact with agonists and antagonists. The most conserved domains of GPCRs are the transmembrane domains and the first two cytoplasmic loops. The transmembrane domains account for structural and functional features of the receptor. In most G-protein coupled receptors, the bundle of a helices forms a ligand-binding pocket formed by several G-protein coupled receptor transmembrane domains.
The TM3 transmembrane domain has been implicated in signal transduction in a number of G-protein coupled receptors. Phosphorylation and lipidation (palmitylation or farnesylation) of cysteine residues can influence signal transduction of some G-protein coupled receptors. Most G-protein coupled receptors contain potential phosphorylation sites within the third cytoplasmic loop and/or the carboxy terminus. For several G-protein coupled receptors, such as the b adrenoreceptor, phosphorylation by protein kinase A and/or specific receptor kinases mediates receptor desensitization. In fact, phosphorylation of an activated G-protein coupled receptor is a common mechanism for desensitizing signaling to a G-protein.
The extracellular N-terminal segment, or one or more of the three hydrophilic extracellular loops, have been postulated to face inward and form polar ligand binding sites which may participate in ligand binding. Ligand binding activates the receptor by inducing a conformational change in intracellular portions of the receptor. In turn, the large, third intracellular loop of the activated receptor interacts with an intracellular heterotrimeric guanine nucleotide binding (G) protein complex which mediates further intracellular signaling activities, including the activation of second messengers such as cyclic AMP (cAMP), phospholipase C, inositol triphosphate, or ion channel proteins. TM3 has been implicated in several G-protein coupled receptors as having a ligand binding site, such as the TM3 aspartate residue. TM5 serines, a TM6 asparagine and TM6 or TM7 phenylalanines or tyrosines have also been implicated in ligand binding (See, e.g., Watson, S. and S. Arkinstall (1994) The G-protein Linked Receptor Facts Book, Academic Press, San Diego Calif., pp. 2–6; Bolander, F. F. (1994) Molecular Endocrinology, Academic Press, San Diego Calif., pp. 162–176; Baldwin, J. M. (1994) Curr. Opin. Cell Biol. 6: 180–190; F Horn, R Bywater, G Krause, W Kuipers, L Oliveira, A C M Paiva, C Sander, G Vriend, Receptors and Channels, 5:305–314, 1998).
Recently, the function of many GPCRs has been shown to be enhanced upon dimerization and/or oligomerization of the activated receptor. In addition, sequestration of the activated GPCR appears to be altered upon the formation of multimeric complexes (AbdAlla, S., et al., Nature, 407:94–98 (2000)).
Structural biology has provided significant insight into the function of the various conserved residues found amongst numerous GPCRs. For example, the tripeptide Asp(Glu)-Arg-Tyr motif is important in maintaining the inactive confirmation of G-protein coupled receptors. The residues within this motif participate in the formation of several hydrogen bonds with surrounding amino acid residues that are important for maintaining the inactive state (Kim, J. M., et al., Proc. Natl. Acad. Sci. U.S.A., 94:14273–14278 (1997)). Another example relates to the conservation of two Leu (Leu76 and Leu79) residues found within helix II and two Leu residues (Leu 128 and Leu131) found within helix III of GPCRs. Mutation of the Leu128 results in a constitutively active receptor—emphasizing the importance of this residue in maintaining the ground state (Tao, Y. X., et al., Mol. Endocrinol., 14:1272–1282 (2000); and Lu. Z. L., and Hulme, E. C., J. Biol. Chem., 274:7309–7315 (1999). Additional information relative to the functional relevance of several conserved residues within GPCRs may be found by reference to Okada et al in Trends Biochem. Sci., 25:318–324 (2001).
GPCRs include receptors for sensory signal mediators (e.g., light and olfactory stimulatory molecules); adenosine, bombesin, bradykinin, endothelin, y-aminobutyric acid (GABA), hepatocyte growth factor, melanocortins, neuropeptide Y, opioid peptides, opsins, somatostatin, tachykinins, vasoactive intestinal polypeptide family, and vasopressin; biogenic amines (e.g., dopamine, epinephrine and norepinephrine, histamine, glutamate (metabotropic effect), acetylcholine (muscarinic effect), and serotonin); chemokines; lipid mediators of inflammation (e.g., prostaglandins and prostanoids, platelet activating factor, and leukotrienes); and peptide hormones (e.g., calcitonin, C5a anaphylatoxin, follicle stimulating hormone (FSH), gonadotropic-releasing hormone (GnRH), neurokinin, and thyrotropin releasing hormone (TRH), and oxytocin). GPCRs which act as receptors for stimuli that have yet to be identified are known as orphan receptors.
GPCRs are implicated in inflammation and the immune response, and include the EGF module containing, mucin-like hormone receptor (Emrl) and CD97p receptor proteins. These receptors contain between three and seven potential calcium-binding EGF-like motifs (Baud, V. et al. (1995) Genomics 26: 334–344; Gray, J. X. et al. (1996) J. Immunol. 157: 5438–5447). These GPCRs are members of the recently characterized EGF-TM7 receptors family. In addition, post-translational modification of aspartic acid or asparagine to form erythro-p-hydroxyaspartic acid or erythro-p-hydroxyasparagine has been identified in a number of proteins with domains homologous to EGF. The consensus pattern is located in the N-terminus of the EGF-like domain. Examples of such proteins are blood coagulation factors VII, IX, and X; proteins C, S, and Z; the LDL receptor; and thrombomodulin.
GPCR mutations, which may cause loss of function or constitutive activation, have been associated with numerous human diseases (Coughlin, supra). For instance, retinitis pigmentosa may arise from mutations in the rhodopsin polynucleotide. Rhodopsin is the retinal photoreceptor which is located within the discs of the eye rod cell. Parma, J. et al. (1993, Nature 365: 649–651) reported that somatic activating mutations in the thyrotropin receptor cause hyperfunctioning thyroid adenomas and suggested that certain GPCRs susceptible to constitutive activation may behave as protooncopolynucleotides.
One large subfamily of GPCRs are the olfactory receptors. These receptors share the seven hydrophobic transmembrane domains of other GPCRs and function by registering G protein-mediated transduction of odorant signals. Numerous distinct olfactory receptors are required to distinguish different odors. Each olfactory sensory neuron expresses only one type of olfactory receptor, and distinct spatial zones of neurons expressing distinct receptors are found in nasal pasages. One olfactory receptor, the RAlc receptor which was isolated from a rat brain library, has been shown to be limited in expression to very distinct regions of the brain and a defined zone of the olfactory epithelium (Raming, K. et al., (1998) Receptors Channels 6: 141–151). In another example, three rat polynucleotides encoding olfactory-like receptors having typical GPCR characteristics showed expression patterns exclusively in taste, olfactory, and male reproductive tissue (Thomas, M. B. et al. (1996) Polynucleotide 178: 1–5).
Although olfactory receptors are typically associated with olfactory function and tend to localize to the olfactory bulb, there is increasing evidence that olfactory receptors and olfactory-like receptors may play more diverse roles in varying tissues (Yuan, T, T., Toy, P., McClary, J. A., Lin, R, J., Miyamoto, N, G., Kretschmer, P, J. Polynucleotide., 278(1–2):41–51, (2001); Blache, P., Gros, L., Salazar, G., Bataille, D, Biochem, Biophys, Res, Commun., 242(3):669–72, (1998); and Matsuoka, I., Mori, T., Aoki, J., Sato, T., Kurihara, K, Biochem, Biophys, Res, Commun., 194(1):504–11, (1993)).
Relaxin is a hormone that belongs to the insulin family of structurally related molecules and was first identified as a factor in pregnany guinea pigs which was capable of lengthening the interpubic ligament of non-pregnant animals. Relaxin has a molecule weight of 6 Kd and consists of two chains, termed A and B which are covalently linked by two interchain disulfide bonds. Relaxin is important for the growth and remodeling of reproductive and other tissues during pregnancy (0. D. Sherwood, in The Physiology of Reproduction, E. Knobil, J. D. Neill, Eds. (Raven, New York, 1994), vol. 1, pp. 861–1009.). Specifically, relaxin has diverse actions in the reproductive tract and other tissues during pregnancy, which include the promotion of growth and dilation of the cervix; growth and quiescence of the uterus; growth and development of the mammary gland and nipple; and regulation of cardiovascular function.
Relaxin has also been shown to play other roles as well, including its role as a vasodilator (Bani and Bigazzi, Acta Anat 119:149–154 (1984); and St. Louis, J. and Massicotte, G., Life Sci., 37:1351–1357 (1985)); and its role in the release of vasopressin from the pituitary gland (Dayanithi, G et al., Nature 325:813–816 (1987)). Additional information specific to relaxin may be found by reference to Dshietzig et al, Cell. Mol. Life Sci. 60:688–700 (2003); which is hereby incorporated by reference herein in its entirety).
Relaxins role in elongating uterine ligaments can be understood at the molecule level based upon the elucidation that it positively regulates matric metalloproteinase expression in uterine segment fibroblasts (Palejwala, S., et al Endo., 142:3405–3413 (2001)). Additionally, relaxins role in vasodilation may be also be understood based upon its upregulation of inducible nitric oxide expression in endothelial cells (Failli, P., et al FASEB J., 16:252–254 (2001)).
Although binding sites for relaxin have been found in reproductive tissues (G. Min and 0. D. Sherwood, Biol. Reprod. 55, 1243 (1996)), brain (P. L. Osheroff and H. S. Phillips, Proc. Natl. Acad. Sci. U.S.A. 88, 6413 (1991)), and heart (P. L. Osheroff, M. J. Cronin, J. A. Lofgren, Proc. Natl. Acad. Sci. U.S.A. 89, 2384 (1992)), the nature of the relaxin receptor had largely been undetermined.
Prorelaxin, the precursor form of relaxin, has a domain arrangement similar to that of insulin and insulin-like growth factor (IGF) precursors, and several relaxin and insulin-related genes have been identified, including those encoding INSL3 (or Leydig cell relaxin), INSL4, INSL5, INSL6, and relaxin 3 (S. Zimmermann, et al., Mol. Endocrinol. 13, 681 (1999); S. Y. Hsu, Mol. Endocrinol. 13, 2163 (1999); and R. A. Bathgate, et al., J. Biol. Chem. 31, 31 (2001)). The abnormal testis descent phenotype of INSL3-null mice (S. Zimmermann, et al., Mol. Endocrinol. 13, 681 (1999), and S. Nef and L. F. Parada, Nature Genet. 22, 295 (1999)) was similar to that of mice with a disruption of a G protein-coupled receptor (GPCR) encoded by the mouse GREAT gene (P. A. Overbeek, et al., Genesis 30, 26 (2001)); which had suggested that relaxin-related proteins may be ligands for GPCRs. Indeed, relaxin stimulates cAMP production in endometrial, anterior pituitary, and other cells (O. D. Sherwood, in The Physiology of Reproduction, E. Knobil, J. D. Neill, Eds. (Raven, New York, 1994), vol. 1, pp. 861–1009), an event mediated by GPCRs.
Recently, two G-protein coupled receptors, referred to as LGR7 and LGR8, were determined to represent relaxin receptors (S. Y. Hsu et al., Science, 295:671–674 (2002)). The role of both GPCRs as relaxin receptors was confirmed based upon experiments demonstrating treatment of transfected cells expressing either LGR7 or LGR8 with porcine relaxin resulted in a dose-dependent increase in cAMP production, with median effective concentrations of 1.5 and 5.0 nM, respectively. The specificity of relaxin to these receptors was tested by subjecting the same transfected cells with peptides that are structurally similar to relaxin, (insulin, IGF-I, or IGF-II) or with an unrelated peptide (glucagon). In all cases, subjecting the cells to these structurally related peptides was ineffective. These findings indicate that relaxin is a cognate ligand for these two orphan GPCRs and that it activates adenylate cyclases through Gs proteins.
Treatment of LGR7 transfected cells with relaxin and the soluble ectodomain (S. Y. Hsu et al., Science, 295:671–674 (2002)) of LGR7 (i.e., a functional LGR7 antagonist) resulted in sequesteration of relaxin and the inhibition of relaxin effects. The same results were obtained by subjecting the transfected cells with relaxin specific antibodies.
Interestingly, subcataneous administration of the LGR7 soluble ectodomain in pregant mice resulted in parturition delay by 27 hours and greatly reduced milk levels in the stomachs of living pups. Furthermore, subcataneous administration of the LGR7 soluble ectodomain in antepartum mice resulted in underdevelopment of nipples, as demonstrated by a 29% decrease in nipple size at 12 hours post parturition. These results were consistent with the nipple development deficiency phenotype observed in relaxin-null knockout mice (L. Zhao, et al., Endocrinology 140, 445 (1999)).
Characterization of the HGPRBMY5v1 and HGPRBMY5v2 polypeptides of the present invention led to the determination that they are involved in the modulation of the p21 G1/S-phase cell cycle check point protein, either directly or indirectly.
Critical transitions through the cell cycle are highly regulated by distinct protein kinase complexes, each composed of a cyclin regulatory and a cyclin-dependent kinase (cdk) catalytic subunit (for review see Draetta, Curr. Opin. Cell Biol. 6, 842–846 (1994)). These proteins regulate the cell's progression through the stages of the cell cycle and are, in turn, regulated by numerous proteins, including p53, p21, p16, and cdc25. Downstream targets of cyclin-cdk complexes include pRb and E2F. The cell cycle often is dysregulated in neoplasia due to alterations either in oncogenes that indirectly affect the cell cycle, or in tumor suppressor genes or oncogenes that directly impact cell cycle regulation, such as pRb, p53, p16, cyclin D1, or mdm-2 (for review see Schafer, Vet Pathol 1998 35, 461–478 (1998)).
P21, also known as CDNK1A (cyclin-dependent kinase inhibitor 1A), or CIP1 inhibits mainly the activity of cyclin CDK2 or CDK4 complexes. Therefore, p21 primarily blocks cell cycle progression at the G1 stage of the cell cycle. The expression of p21 is tightly controlled by the tumor suppressor protein p53, through which this protein mediates the cell cycle G1 phase arrest in response to a variety of stress stimuli. In addition, p21 protein interacts with the DNA polymerase accessory factor PCNA (proliferating cell nuclear antigen), and plays a regulatory role in S phase DNA replication and DNA damage repair.
After DNA damage, many cells appear to enter a sustained arrest in the G2 phase of the cell cycle. Bunz et al. (Science 282, 1497–1501 (1998)) demonstrated that this arrest could be sustained only when p53 was present in the cell and capable of transcriptionally activating the cyclin-dependent kinase inhibitor p21. After disruption of either the p53 or the p21 gene, gamma-radiated cells progressed into mitosis and exhibited a G2 DNA content only because of a failure of cytokinesis. Thus, p53 and p21 appear to be essential for maintaining the G2 cell cycle checkpoint in human cells.
Due to the connection between the transcriptional activity of p53 and p21 RNA expression, the readout of p21 RNA can be used to determine the effect of drugs or other insults (radiation, antisense for a specific gene, dominant negative expression) on a given cell system which contains wild type p53. Specifically, if a gene is removed using antisense products and this has an effect on the p53 activity, p21 will be upregulated and can serve therefore as an indirect marker for an influence on the cell cycle regulatory pathways and induction of cell cycle arrest.
In addition to cancer regulation of cell cycle activity has a role in numerous other systems. For example, hematopoietic stem cells are relative quiescent, while after receiving the required stimulus they undergo dramatic proliferation and inexorably move toward terminal differentiation. This is partly regulated by the presence of p21. Using p21 knockout mice Cheng et al. (Science 287, 1804–1808 (2000)) demonstrated its critical biologic importance in protecting the stem cell compartment. In the absence of p21, hematopoietic stem cell proliferation and absolute number were increased under normal homeostatic conditions. Exposing the animals to cell cycle-specific myelotoxic injury resulted in premature death due to hematopoietic cell depletion. Further, self-renewal of primitive cells was impaired in serially transplanted bone marrow from p21−/− mice, leading to hematopoietic failure. Therefore it was concluded that p21 is the molecular switch governing the entry of stem cells into the cell cycle, and in its absence, increased cell cycling leads to stem cell exhaustion. Under conditions of stress, restricted cell cycling is crucial to prevent premature stem cell depletion and hematopoietic death. Therefore, genes involved in the downregulation of p21 expression could have a stimulatory effect and therefore be useful for the exploration of stem cell technologies.
Using the above examples, it is clear the availability of a novel cloned G-protein coupled receptor provides an opportunity for adjunct or replacement therapy, and are useful for the identification of G-protein coupled receptor agonists, or stimulators (which might stimulate and/or bias GPCR action), as well as, in the identification of G-protein coupled receptor inhibitors. All of which might be therapeutically useful under different circumstances.
The present invention also relates to recombinant vectors, which include the isolated nucleic acid molecules of the present invention, and to host cells containing the recombinant vectors, as well as to methods of making such vectors and host cells, in addition to their use in the production of HGPRBMY5v1 and HGPRBMY5v2 polypeptides or peptides using recombinant techniques. Synthetic methods for producing the polypeptides and polynucleotides of the present invention are provided. Also provided are diagnostic methods for detecting diseases, disorders, and/or conditions related to the HGPRBMY5v1 and HGPRBMY5v2 polypeptides and polynucleotides, and therapeutic methods for treating such diseases, disorders, and/or conditions. The invention further relates to screening methods for identifying binding partners of the polypeptides.